This invention relates to a method for suppressing the formation of sulfuric acid aerosols in exhaust gas purification systems. The exhaust gas is presprayed with water such that the temperature does not drop below the dew point of sulfuric acid in the exhaust gas. In this manner, gaseous sulfuric acid is absorbed by the water thereby preventing the formation of sulfuric acid aerosols which can lead to corrosion and emission problems.
To separate sulfur dioxide and sulfur trioxide from exhaust gases produced in the burning of fossil fuels or incineration of refuse in power plants or incinerator systems, sulfur is removed from the exhaust gas. The emission of these substances is reduced drastically by exhaust gas desulfurization to prevent these substances from becoming environmental pollutants.
The most important exhaust gas desulfurization methods are scrubbing methods using suspensions of limestone or hydrated lime. With these so-called wet methods, the exhaust gases are treated with an atomized scrubbing suspension while cooling in spray towers, so that more than 95% desulfurization can be achieved.
In addition to sulfur dioxide, combustion exhaust gases also contain sulfur in the form of gaseous sulfuric acid, which is in gas form when exhaust gas temperatures are above the dew point of sulfuric acid (approx. 130.degree. C.).
Sulfuric acid aerosols are formed by rapid cooling of exhaust gas in gas scrubbers to temperatures of 45.degree. C. to 65.degree. C. Sulfuric acid aerosols are extremely fine droplets of highly concentrated sulfuric acid which are not separated in the scrubber or in downstream mist collectors. Thus, the downstream stages of an exhaust gas purification system are being supplied with liquid sulfuric acid which can be removed completely only at great expense.
Sulfuric acid aerosols lead to emission and corrosion problems. Corrosion problems occur, first, due to acid attacking ducts and equipment in the clean gas pathways downstream from the flue gas scrubbers and upstream from the chimney. Second, problems have occurred in the vicinity of coal-burning power plants in the past due to emission of acid particles.
It is essentially known from German Patent DE 4,125,214 A1 that gas mixtures can be subjected to prespraying with water (quenching) before gas scrubbing in a scrubbing tower. In the known methods, however, the aforementioned rapid drop in temperature is associated with the development of a sulfuric acid aerosol.